I understand it's different modelling technology but they are modelling the same amp at the same settings, so there shouldn't be (much) difference unless you're saying that one is more/less accurate. Or am I missing something?

Hi. As far as I know, Spotify doesn't work (for selecting songs from within the FH app).
You can play any audio (music, audiobooks,YouTube, whatever) through the FHFX over bluetooth.
I've not tried the return of the fx loop for music. I'm not sure it would work as the FH will be sending part of your guitar signal off to the loop but it won't return so that might affect the guitar signal. I think it is something you could try but don't be surprised if it doesn't work out.
Whether you use your amp, home stereo or headphones is up to you. You should get better results from the home stereo/headphones, if you're playing along to a backing track through the FH. If you use the katana, use the 4 cable method and disable amp and cab sims on the FH.
As far as we know, there aren't any updates on the horizon so if you buy one, perhaps accept the unit for what it does now and if they provide more amps/effects later then that's cool. Just don't bank on it.

I've had my FHFX for 18 months. I like the FHFX and enjoy building and tweaking patches. I like the ipad app and I find it easy to use. My FHFX is nowhere near a pc so I don't miss the fact that there is no pc editor. If that's what I wanted, I would have gone down the HD500X route.
I would like to see some more updates - I want them to add more amps and effects but that probably won't happen. Do your research first so you know what you're getting into. If you are happy with what the FHFX has to offer then now would be the best time to do it. In the UK they have been reduced to Â£249 which is Â£100 cheaper than the HD500X.
Best of luck and Merry Christmas.

I've got to be honest, I had this problem when I first updated but I can't remember what I did to get around it. Sorry!
Yes, there should be a bar that moves along/fills up as the download and update applies. I think there might also be some text to confirm it is progress.
You could try everything from scratch (reinstall app, forget and re-pair bt, make sure you back up all tones and reset FH unit to factory settings) then try it again. But it seems as though you've pretty much tried everything.
If you're still struggling, might be an idea to open a support ticket to get L6 on board - http://line6.com/support/tickets/
Best of luck.

I've always updated mine using my iPad over bt and thankfully it's worked fine. I do recall that it took a while though. Have you tried letting it run for a while to see if it does update (could be dependent on download speed, server use or whatever). If not, reinstall FH app and retry.
On your pic, is there an option to reinstall/repair the OpenGL 2.0 driver? Could it be that it is corrupted?
I don't recall any noticeable difference to my FHFX after updating to 1.30 so I doubt you're missing out, but it would frustrate me if I couldn't do it.

Hi. Select Bender as a pedal in your patch.
On the Bender options screen, press and hold anywhere on the Position slider bar on your iPad and a box pops up asking if you want to assign tweak to the Position parameter. Yes.
Then there will be an option below the bar to assign it to the pedal. Yes (btw No means that you control it with the fx knob).
Then mess with your sliders to get the effect you want - toe 0, heel -12? I don't know. Whatever gets you the effect you're after.
I hope that helps.

If Cloud is greyed out it suggested that you are not signed in/connected to Line 6. In that case you would have to sign in and then make your changes or make the changes on the unit. Just remember that you will probably want to back up any changes when you next connect.

I only ask because I noticed that although Thomann carry lots of L6 products they now say -
"Sorry! The item Line6 Firehawk FX is not part of our current product range anymore"
Same with Firehawk 1500. Maybe it's only a temporary thing but I wonder whether anyone else has better info. I see that UK sellers still have stock. Apologies if this comes across as scaremongering.